Field of the Invention
The present invention relates generally to safety devices for internal combustion engine powered implements and more particularly to such safety devices which function to promptly stop the engine in the event that the implement operator moves from his normal operating position. Even more specifically, the present invention is concerned with an improved linkage arrangement for such safety devices requiring a relatively constant operator actuating force.
The need for safety devices for power driven implements to reduce the probability of injury to the operator or others has long been recognized and a wide variety of such safety devices are known. The provision of a protective shield or shroud around dangerous moving parts is commonplace as is the automatic disabling of a dangerous implement when its normal operating mode is interrupted.
A typical illustration of the disabling type safety device is the so-called deadman lever. Such levers are frequently employed on the handle of lawnmowers, garden tillers, snowblowers, and the like, and require the operator to be gripping the handle and depressing the lever against a normal spring bias to render the device operational. In the event that the operator releases his grip on the handle, the deadman lever moves typically away from the handle to a position to disable the device. One such known deadman level disables the ignition circuit on an internal combustion engine rotary lawnmower. Another known deadman lever arrangement is connected to an idler wheel or pulley in the V-belt drive arrangement for a garden tiller with that pulley spring biased toward a position away from the V-belt. Under these conditions the V-belt drive is interrupted since the belt is larger than required to connect the engine to the tiller moving parts and only when the deadman lever is depressed forcing the pulley into engagement with the V-belt and removing slack from the V-belt drive is the tiller operational.
Another known application of a deadman lever to a power driven implement is the interposition of a clutch brake arrangement between the power source such as an internal combustion engine and the dangerous implement such as the rotating blade of a rotary lawnmower or snowthrower. The deadman lever when depressed actuates the clutch to couple the power source to the rotating blade, while when the lever is released the clutch is disengaged and a brake actuated to stop the rotating blade.
It would be highly desirable to retain the advantages of the deadman level type safety device without the necessity of providing a clutch drive between the power source and the dangerous instrumentality and further highly desirable to reduce as far as possible the time interval between the release of the deadman lever and the stopping of the dangerous instrumentality. It would also be highly desirable to provide a safety device wherein the operator must return to his normal operating position before the instrumentality may be reenergized. These desires, as well as others, have been achieved in co-pending U.S. patent application Ser. No. 205,010, filed Nov. 7, 1980, the entire disclosure of which is specifically incorporated herein by reference.
Briefly, in the aforementioned co-pending application, flywheel braking is achieved upon the release of a deadman control by pivoting a braking member into engagement with a lower annular surface of the flywheel or by moving the braking member generally parallel to the flywheel lower annular surface and into engagement therewith by a ramp arrangement forcing the braking member toward the flywheel surface. In either case, the force between the braking member and the flywheel surface is the force determined by the spring or other arrangement forcing those two surfaces together, and it is this same force which must be overcome by the operator when actuating the deadman lever to disengage the brake, and it would be highly desirable to provide the advantages and safety features of the aforementioned co-pending application while reducing the force required on the deadman control to maintain the brake arrangement disengaged.
This further desire has been realized in co-pending U.S. patent application Ser. No. 321,769, filed Nov. 16, 1981, wherein upon initial engagement between a flywheel braking surface and a brake pad the continued flywheel rotation induces additional movement of the brake pad wedging the friction surface of that pad more tightly against the flywheel thereby increasing the braking force. Thus, in the improvement represented by this co-pending patent application the strength of the spring against which the operator must hold the deadman lever during implement operation has been reduced; however, the system still generally follows Hooke's Law in that the stress or applied force on the deadman lever is directly proportional to the strain or resulting deformation of the spring biasing the braking member. Thus, while the overall strength of the spring has been reduced in this last-mentioned improvement, the operator still encounters successively greater resistance to actuation of the deadman lever the further that lever is moved against the spring biasing force. It would be highly desirable to provide a deadman lever-type safety device having the advantages of this last-mentioned co-pending application while circumventing Hooke's Law in the sense that the force the operator must apply to the deadman lever remains substantially constant regardless of the distance that lever is moved. It would also be highly desirable to retain the starting feature of the last-mentioned co-pending application wherein the Bowden cable coupling the deadman lever to the brake mechanism may be additionally moved by a second operator actuable control so as to place the engine in an electric start mode when the deadman lever is depressed by the operator. Accordingly, the entire disclosure of co-pending U.S. patent application Ser. No. 321,769, filed Nov. 16, 1981, is specifically incorporated herein by reference.